London has been battered by 50mph winds that have felled trees and caused travel chaos. Powerful gusts swept across the capital as the Met Office issued a yellow "be aware" weather alert for most of the country.

The Government should honour its pledge to safeguard the Green Belt in the face of plans for thousands of new homes and other development on protected land, campaigners have said.

The Campaign to Protect Rural England claimed Green Belt land around cities and towns across England was under threat from bids to build more than 81,000 homes, as well as new roads, industrial parks, mines and airport expansion.

Proposals which are out for consultation, been submitted for planning permission or have been approved would cover Green Belt land equivalent to a new town larger than Slough, it suggested. According to CPRE, plans include the expansion of Birmingham Airport, proposals for freight terminals near St Albans, Luton and St Helens, an open cast coal mine at Broxtowe, Nottinghamshire, and a hotel and golf course at Leatherhead, Surrey.

Green Belt land around the country is also under threat from more than 1,000 hectares (2,500 acres) of business and industrial parks and housing developments each with hundreds or even thousands of new homes, said CPRE.

The Government has committed to protecting the Green Belt, which makes up 12% of English land, from development, although reform of the planning system this year prompted concerns protection for the wider countryside would be weakened.

Under the new planning policy, local authorities are required to allocate more than five years' worth of building land for new housing, and CPRE warned councils are under pressure to allow building in the Green Belt to meet the target. And there have been renewed fears in recent weeks over the protection of the Green Belt, amid suggestions planning laws could be relaxed to boost economic growth.

Paul Miner, senior planning officer for the campaign group, said: "In times of economic slowdown, politicians can sometimes be tempted by the false promise of an easy construction boom. But destroying the countryside is not the path to lasting economic prosperity. Sustainable economic improvement can only come from the sort of urban regeneration that has already done much to rejuvenate many of our largest cities."

He added: "Ministers have consistently maintained that they value the Green Belt and want to see it protected. Now is the time to put these words into action."

A spokesman for the Department for Communities and Local Government said: "The Green Belt is an important protection against urban sprawl, providing a 'green lung' around towns and cities. The Coalition Agreement commits the Government to safeguarding Green Belt and other environmental designations, which they have been in the new National Planning Policy Framework.

"The Government is giving local communities a greater say on planning and is scrapping top-down targets. The Localism Act allows for the abolition of Regional Spatial Strategies which sought to bulldoze the Green Belt around 30 towns and cities across the country."